This invention refers to aluminum chloride and more particularly to a method of forming aluminum chloride.
Because of the interest which has existed through the years in aluminum chloride as a catalyst and in the possibility of electrolytically producing aluminum from aluminum chloride, considerable effort has been expended to produce aluminum chloride in a highly economical manner. Production of such aluminum chloride by the reduction of alumina-containing materials with a source of chlorine and in the presence of a solid reducing agent such as carbon, or a gaseous reducing agent such as carbon monoxide is known in the art.
For example, Hille et al in The Production of Anhydrous Chloride from .gamma.-Alumina in a Fluidized Bed, Angew. Chem. Internat. Edit. Vol. 72, 1960, pp. 73-79, teach the reaction of an alumina-containing material such as bauxite or clay with chlorine gas in the presence of a gaseous or solid reducing agent in a shaft furnace as well as the reaction of gamma alumina with chlorine gas in the presence of carbon monoxide in a fluidized bed.
It is well known that alumina will dissolve in cryolite or alkali halide. Thus, it was proposed by Hall in U.S. Pat. No. 1,405,115 that aluminum chloride be formed by passing chlorine and sulfur gases through such a mixture. However, such a method can result in channeling of the gaseous reactants with the result that either one of the gases may not contact both the alumina and the other gas in which instance the aluminum chloride yield may be quite low.
Russell et al in U.S. Pat. No. 3,842,163 teach and claim the production of a high purity aluminum chloride useful in the electrolytic production of aluminum by feeding a substantially pure alumina coated or impregnated with carbon into a fluidized bed with chlorine gas to produce aluminum chloride. However, this process requires a preliminary step to coat or impregnate the alumina with carbon.
It has also been suggested in German Patentschrift No. 842,986 that the addition of alkali chlorides has a favorable effect on a process in which alumina is contacted with phosgene or chlorine and carbon monoxide.
Groshev et al in The Chlorination of Oxides of the Residue from a Shaft Furnace which Produces Anhydrous Aluminum Chlorides the Oxides being Suspended in a Medium of Molten Chlorides, Tr. po Khim, i Khim. Technol. 3, 344-351 (1960), teach chlorinating the residue of a shaft furnace to produce aluminum chloride and iron-free silicon tetrachloride using coke oil and chlorine. A batch of the residue is suspended in a molten bath of KCl, NaCl and AlCl.sub.3. However, according to this article, only 50% of the chlorine added is converted, i.e. presumably a 50% yield. Coke oil present in an amount over 5% is stated to have no effect on increasing the yield. The article also states that the absence or presence of AlCl.sub.3 up to 69.5% has no effect on the chlorination. Size of particles of the solid phase does not affect chlorination either according to the article.
Such processes, however, while producing high purity aluminum chloride suitable for use as Friedel-Crafts catalyst or for electrolytic production of aluminum, often are not very efficient and may generate effluent dust which then must be removed before the AlCl.sub.3 is condensed.
Quite surprisingly we have discovered a system for producing aluminum chloride in a molten salt bath which solves or eliminates most of these problems. For example, the process is highly economical in that chlorine conversion can be 100% eliminating waste of the chlorine or subsequent separation steps. Also, this yield can be achieved using low surface area alumina which is generally considered to be less reactive.